[clang] [Clang] Implement C++26’s P2893R3 ‘Variadic friends’ (PR #101448)

[Younan Zhang via cfe-commits]

https://github.com/zyn0217 commented:

Thanks so much for continuing the effort to implement this! I haven't dived into the details yet, so here are some nits from me.

(I'd also prefer the pronouns he/him if you'd like. ;)

https://github.com/llvm/llvm-project/pull/101448